The present invention relates to modems and to communications networks. In particular, this invention relates to the use of 208B compatible modems and V.32 compatible modems in the same communications network.
Currently, there are a number of communications networks that are built around the 208B type of modem, which transfers data via a half-duplex signaling scheme at a transmission speed of 4800 bits per second (sec.). One example of such a communications network is the Electronic Data Interchange (EDI) network, which may be used by a business to distribute billing and inventory to its various locations. In addition, some states provide a half-duplex communications network to allow insurance carriers to gain access to a state's division of motor vehicles data base to get information on licensed drivers within a state.
However, the 208B type of modem has been around for a long time and in comparison to a state-of-the-art modem, like the V.32 modem, it has a lower data throughput. For example, the V.32 modem can transfer data via a full-duplex signaling scheme and has a transmission speed of 9600 bits per second. Further, the V.32 bis modem is also full-duplex and additionally increases the transmission speed to 14,400 bits per second. Unfortunately, a V.32 type of modem will not connect to a 208B modem. As a result, customer's who have networks comprising 208B modems can only upgrade to a V.32 type of modem by changing out their entire network of modems--at a large cost.
There have been some attempts in the prior art to deal with communications networks comprising different types of modems. One manufacturer sells a modem that can provide either a 208B mode of operation or a V.32 mode of operation. However, the particular mode of operation of this modem is determined by the adjustment of a hardware swap. In other words, the customer must physically access the modem and change a switch setting on the modem. Consequently, this requires that the mode of operation must be determined before even attempting to establish a connection to another modem. Therefore, the customer must know ahead of time the identity of the other modem, i.e., whether it is a 208B type of modem or a V.32 type of modem. While this may be feasible for originating a data call to another modem, this may not be a practical for answering a data call from another modem.
In comparison, U.S. Pat. No. 4,215,243, issued Jul. 29, 1980 to Maxwell discloses a central facility that is capable of receiving data calls that may originate from different types of modems. The central facility, which also comprises a modem pool that includes a number of different types of modems, identifies the calling modem by detecting the frequency of the originating carrier after the central facility has provided an answer tone. Once the calling modem has been identified the central facility connects the calling modem to a respective modem of the same type in its modem pool.
Unfortunately, the approach of the Maxwell reference does not adequately address the problem of switching between a V.32 mode and a 208B mode. In particular, the procedure of the Maxwell reference would have difficulty working in a V.32 modem environment because it occurs too late in the connect sequence, i.e., after the answer tone has been provided, and it provides no way to vary the answertone in the connect sequence. In addition, it also presents a solution that requires a central location with a diverse modem pool, i.e., it relies on the presence of different type of modems in its modem pool to complete the data connection sequence. Finally, it does not address the situation where the central site originates the data call, or where a single modem either originates or answers a data call.